The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present disclosure.
Microfluidic devices, such as micro-structured polymer devices (MPDs), are useful tools for the analysis of chemicals and biological fluids. Microfluidic devices can be formed from plastics compounds, which may be formed by a moulding process. Microfluidic devices typically include fluid transport channels—for example input and output channels—and other fluid flow or storage structures to enable the intended measurement or chemical or biological reaction to take place. For effective analysis of the fluid by the microfluidic device the fluid must controllably pass through these channels.
Microfluidic devices will often include electrodes, i.e. electrically conductive structures, arranged to interact with fluid in the channels or other fluid structures. Examples might be electrodes leading to a measurement sensor, to enable a property of a channel to be measured, and electrodes for receiving an active electrical stimulus, e.g. to receive a voltage signal for manipulating fluid in the MPD by electrowetting or dielectrophoresis.
Various types of microfluidic devices have been proposed. The channel cross-section dimensions in a microfluidic device can vary widely, but may be anything from the millimetre scale to the nanometre scale. Reference to microfluidics in this document is not restricted to micrometre scale devices, but includes both larger (millimetre) and smaller (nanometre) scale devices as well as intermediate (micrometre) scale devices, as is usual in the art.
A basic form of a microfluidic device is based on continuous flow of the relevant fluids through the channels.
A development of this basic form has the active fluid conveyed through the channels in droplets held in suspension by a functionally inert carrier liquid. Some of the devices described herein are droplet-based, microfluidic devices. In such devices, a droplet is formed of a first liquid, the droplet liquid, suspended immiscibly in a second liquid, the carrier liquid. The droplet liquid and the carrier liquid should be selected to be immiscible over the relevant time scale needed for good functioning of the device as determined by factors such as transit time, storage time, and reaction time within the device. Droplets are generally spherical, but in use the droplets may be distorted by forces or constrained by boundaries of the channel or other parts of the microstructured device, so other shapes may exist. A droplet in the context of a digital microfluidic device is therefore a contiguous volume of a fluid held in a carrier liquid, wherein the fluid and the carrier liquid are immiscible.
Microfluidic devices may be made from a variety of substrate materials, including thermoplastic, glass and crystal. In thermoplastic microfluidic devices, the channels can be formed by a variety of means, including injection moulding.
Known ink compositions contain non-volatile solvents, particularly high boiling point polyols such as glycerol. The boiling point of these solvents may range from 80 to 300° C., in some embodiments 100 to 200° C. These components act as humectants to prevent premature drying of the ink in the jetting nozzles to ensure reliability of the jetting process. The sintering is normally a heating step which evaporates the solvent of the conductive liquid. The presence of the high boiling point liquids influences the temperature of the sintering however as any remaining organic component will impede a conductive pathway, thereby producing a product with lower and more variable conductivity. Higher sintering temperatures require a greater energy input and may damage thermoplastic substrates.
It is to be understood that both the foregoing general description of the disclosure and the following detailed description are exemplary, but are not restrictive, of the invention disclosure.